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FOC | Family List | FOC Vol. 14 | Apiaceae

12. Rhododendron Linnaeus, Sp. Pl. 1: 392. 1753.

杜鹃属 du juan shu

Fang Mingyuan (方明渊), Fang Ruizheng (方瑞征 Fang Rhui-cheng), He Mingyou (何明友), Hu Linzhen (胡琳贞 Hu Ling-cheng), Yang Hanbi (杨汉碧 Yang Han-pi); David F. Chamberlain

Rhododendron aganniphum var. schizopeplum

Credit: Harvard University Herbaria

Shrubs or trees, terrestrial or epiphytic, with various hairs, and/or with peltate scales or glabrous, indumentum sometimes detersile (the hairs tangled and coming away as a layer). Leaves evergreen, deciduous or semideciduous, alternate, sometimes clustered at stem apex; margin entire, very rarely crenulate, abaxial indumentum sometimes with a pellicle (a thin skinlike layer on the surface). Inflorescence a raceme or corymb, mostly terminal, sometimes lateral, few- to many-flowered, sometimes reduced to a single flower. Calyx persistent, 5–8-lobed, sometimes reduced to a rim, lobes minute and triangular to large and conspicuous. Corolla funnelform, campanulate, tubular, rotate or hypocrateriform, regular or slightly zygomorphic, 5(–8)-lobed, lobes imbricate in bud. Stamens 5–10(–27), inserted at base of corolla, usually declinate; filaments linear to filiform, glabrous or pilose towards base; anthers without appendages, opening by terminal or oblique pores. Disk usually thick, 5–10(–14)-lobed. Ovary 5(–18)-locular, with hairs and/or scales, rarely glabrous. Style straight or declinate to deflexed, persistent; stigma capitate-discoid, crenate to lobed. Capsule cylindrical, coniform, or ovoid, sometimes curved, dehiscent from top, septicidal; valves thick or thin, straight or twisted. Seeds very numerous, minute, fusiform, always winged, or both ends with appendages or thread-like tails.

About 1000 species: Asia, Europe, North America, two species in Australia; 571 species (409 endemic) in China.


1 Inflorescence buds lateral, usually in axils of upper or lower leaves of last year’s shoots; uppermost inflorescence buds (or leaf bud) in axils of uppermost leaves, subterminal.   (2)
+ Inflorescence buds terminal, sometimes with additional lateral floral buds immediately below, vary rarely axillary from lower leaves (as in some species of R. subsect. Cinnabarina).   (4)
       
2 (1) New foliage shoots from axils of leaves below inflorescence buds; leaves with peltate scales, deciduous or semievergreen; flowers appearing before leaf emergence.   4 Rhododendron subg. Rhodorastrum
+ New foliage shoots arising from uppermost (pseudoterminal) buds, and from axils of leaves; leaves evergreen.   (3)
       
3 (2) Plants with peltate scales; capsule short, cylindric.   3 Rhododendron subg. Pseudorhodorastrum
+ Plants without peltate scales; capsule conical-ovoid or cylindric.   6 Rhododendron subg. Azaleastrum
       
4 (1) Plant with peltate scales, sometimes also with other hairs.   (5)
+ Plant without peltate scales, with various hairs, or glabrous.   (6)
       
5 (4) Leaves evergreen, very rarely semideciduous to deciduous; flowers appearing after leaf emergence; style usually straight; plant usually without hairs.   1 Rhododendron subg. Rhododendron
+ Leaves deciduous or semideciduous, very rarely evergreen; flowers appearing before leaf emergence; style usually short and recurved; plant usually hairy.   2 Rhododendron subg. Pseudazalea
       
6 (4) Corolla divided nearly to base on lower side; peduncle bearing leafy bracts; style curved.   9 Rhododendron subg. Therorhodion
+ Corolla not divided to base; peduncle without bracts; style slender, straight.   (7)
       
7 (6) Flowers and new leafy shoots from same terminal buds; leaves persistent to deciduous; indumentum often with strap-shaped setae.   8 Rhododendron subg. Tsutsusi
+ Flowers from terminal buds; new leafy shoots from lateral buds, i.e., from axils of leaves of previous season; indumentum without flattened setae.   (8)
       
8 (7) Leaves evergreen; stamens 10(–20)   5 Rhododendron subg. Hymenanthes
+ Leaves deciduous; stamens 5 (in Chinese species).   7 Rhododendron subg. Pentanthera

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